The invention relates generally to construction vehicles having adjustable height suspensions. More particularly, it relates to skid steer vehicles having sprung suspensions that are continuously adjustable to automatically accommodate changes in vehicle loads.
Skid steer vehicles such as skid steer loaders are used in a wide variety of construction environments where they are particularly suitable due to their small size and maneuverability.
Skid steer vehicles can turn with an effective turning radius of zero. They can rotate about a vertical axis extending through the center of the chassis by driving the wheels on one side of the vehicle forward and the wheels on the other side of the vehicle backwards. Since the wheels cannot be steered with respect to the chassis, this causes the wheels to skid sideways as they rotate. This is the extreme case. Even when the vehicle is moving forward or backward (i.e. the wheels on both sides of the vehicle are driven in the same direction) the vehicle still steers by skidding, albeit to a lesser degree.
Skid steer vehicles are well suited to work on construction sites and even within buildings due to this ability to skid steer. Enhancing this capability is their compact size. Skid steer vehicles have a compact wheelbase, on the order of 40 to 50 inches with a typical wheel diameter of between 28 and 32 inches and a width over wheels of between 60 and 80 inches. Unlike many work vehicles, the wheelbase is typically less than two wheel diameters. More typically, it is on the order of 1.25 to 1.75 diameters.
This close wheel spacing front-to-back and side-to-side has effectively prevented the use of sprung suspensions on skid steer vehicles.
First, the addition of a suspension is difficult due to the compact size of the skid steer vehicle itself. Adding suspensions would increase the width of the vehicle and make it less suitable for the close spaces in which it is used.
Second, traditional automotive-type suspensions would cause excessive pitching of the work vehicle, given its short wheelbase (e.g. vehicles having a front-to-rear wheel spacing of less than two wheel diameters).
For example, a typical automotive or truck type passive suspension includes a vertically oriented spring that is coupled to the chassis at its upper end. The point of coupling is typically directly above the rotational axis of the wheel supported on that suspension. As a result, whenever the wheel is forced upward, (such as when the car goes over a bump) the spring is compressed, and an upward force is applied to the chassis directly above the wheel where the spring is anchored.
To illustrate the problem, consider a skid steer loader with loader arms that support a bucket. When the bucket is loaded with dirt or other material and the vehicle is driven over rough ground, the increased load on the front of the vehicle would cause the front suspensions to squat as they are compressed by the additional load.
Given the limited ground clearance of a skid steer loader and the short wheelbase, this forward pitch due to the increase of the static load would be significant and would cause material to be dumped from the bucket. In addition, it could cause the vehicle, when pitching fore-and-aft, to collide with the ground. Furthermore, any additional load placed on a skid steer loader, even if it does not pitch, will reduce ground clearance generally.
Thus, one of the reasons that skid steer vehicles have not been equipped with suspensions is due to the inability of a standard passive suspension to accommodate the compression and extension of the suspension under changing loads. This is a problem peculiar to skid steer loaders or other skid steer vehicles and has prevented the development of practical suspension systems for skid steer loaders.
What is needed therefore, and what is provided by the present invention, is a sprung suspension system coupled to controls that level a skid steer vehicle automatically and dynamically under changing load conditions. What is also needed is a sprung suspension system for a skid steer loader that senses the pitch and height of the vehicle and automatically raises and lowers the suspensions to level the vehicle. What is also needed is a sprung suspension system that can raise and lower the chassis to maintain a constant ground clearance. It is an object of this invention to provide such a skid steer vehicle.
In accordance with a first embodiment of the invention, a skid steer vehicle is provided that includes a chassis having a left side and a right side; an engine fixed to the chassis; a first hydraulic fluid pump driven by the engine to provide hydraulic fluid under pressure; a second hydraulic fluid pump driven by the engine to provide hydraulic fluid under pressure; a third hydraulic fluid pump driven by the engine to provide hydraulic fluid under pressure; at least a first hydraulic motor in fluid communication with the first hydraulic fluid pump; at least a second hydraulic motor in fluid communication with the second hydraulic fluid pump; left front and left rear suspensions mounted in a fore-and-aft arrangement on the left side of the chassis for pivotal movement with respect thereto, each left suspension including a left ground-engaging wheel extending from the left side of the chassis and rotationally coupled to the at least a first hydraulic motor to be driven in rotation thereby, a left control arm assembly coupled to and between the left wheel and the chassis, a left hydraulic cylinder disposed between the chassis and the left control arm such that movement of the left control arm with respect to the chassis causes the left cylinder to extend and retract, a hydraulic valve coupled to and between the left hydraulic cylinder and the third hydraulic pump to regulate the flow of fluid from the third hydraulic pump to the left hydraulic cylinder, and a left suspension sensor that is responsive to changes in the position of the suspension to generate a signal indicative of the position of the suspension with respect to the chassis; right front and right rear suspensions mounted in a fore-and-aft arrangement on the right side of the chassis for pivotal movement with respect thereto, each right suspension including a right ground-engaging wheel extending from the right side of the chassis and rotationally coupled to the at least a second hydraulic motor to be driven in rotation thereby, a right control arm coupled to and between the right wheel and the chassis, a right hydraulic cylinder disposed between the chassis and the right control arm such that movement of the right control arm with respect to the chassis causes the right cylinder to extend and retract, a hydraulic valve coupled to and between the right hydraulic cylinder and the third hydraulic pump to regulate the flow of fluid from the third hydraulic pump to the right hydraulic cylinder, and a right suspension sensor that is responsive to changes in the position of the suspension to generate a signal indicative of the position of the right suspension with respect to the chassis; and an electronic controller electrically coupled to the left front, left rear, right front and right rear suspension sensors to receive the signals indicative of the positions of those suspensions and coupled to the left front, left rear, right front and right rear suspension hydraulic valves to regulate hydraulic fluid flow from the third hydraulic fluid pump into the cylinders responsive to signals received from the suspension sensors.
The electronic controller may be configured to determine the height of each suspension, to compare the determined height of each suspension with a predetermined height value, and to fill the hydraulic cylinder associated with any suspension that is below a predetermined height. The electronic controller may fill the hydraulic cylinder by opening the hydraulic valve associated with that suspension. The electronic controller may be configured to receive a plurality of the signals indicative of suspension position from each of the suspension sensors and to derive for each suspension a single position value indicative of suspension height from said plurality of signals. The electronic controller may be configured to repeatedly and automatically poll the position signals provided by the left front, left rear, right front and right rear suspension sensors at predetermined polling rate of no less than 1 Hertz.
In accordance with a second embodiment of the invention, a method for controlling the height of a skid steer vehicle is provided, the skid steer vehicle having an electronic suspension controller, a chassis with a left side and a right side and four independent sprung suspensions, two disposed on each side of the vehicle in a fore-and-aft relation, each of the four suspensions including a hydraulic cylinder operatively coupled between the suspension and the chassis to raise and lower said each suspension with respect to the chassis, each suspension also including a suspension sensor configured to generate a signal indicative of suspension height with respect to the chassis, wherein the wheels on the left side of the vehicle are configured to be driven by at least a first hydraulic motor and the wheels on the right side of the vehicle are configured to be driven by at least a second hydraulic motor, and further wherein the wheels on the left side and the wheels on the right side can be driven in opposing rotational directions, the method including the steps of receiving a first position signal indicative of a first position of a first of the four suspensions with respect to the chassis from the suspension sensor of the first suspension; comparing a first position value derived from at least the first position signal with a predetermined value indicative of a desired suspension position; raising the first suspension when the step of comparing indicates that the first suspension is below the desired first suspension position and lowering the first suspension when the step of comparing indicates that the first suspension is above the desired first suspension position. Each of the steps in the foregoing sentence may be repeated for each suspension of the vehicle. The method may include the steps of receiving a second position signal indicative of a second position of the first suspension with respect to the chassis from the suspension sensor of the first suspension; and combining the first and the second position signals to generate the first position value. The step of combining may include the step of averaging the first and second position signals to generate the first position value.
In accordance with a third embodiment of the invention, a work vehicle is provided that includes a chassis having a left side and a right side; an engine coupled to the chassis; four non-steerable and ground-engaging wheels coupled to the chassis to drive the vehicle over the ground, wherein the wheels are disposed two on each side of the chassis in a fore-and-aft relation; at least two hydraulic motors for driving the wheels wherein at least one motor drives the wheels on one side of the chassis and at least another motor drives the wheels on the other side of the chassis; four position sensors disposed to sense the vertical position of the wheels with respect to the chassis; four hydraulic actuators, each actuator coupled to one of the wheels, to control the position of the wheels with respect to the chassis; and an electronic controller coupled to both the position sensors and the actuators to monitor the position of each wheel with respect to the chassis and to raise and lower said each wheel at least in response to position signals received from the position sensors.
The chassis may be supported on the ground only by the four wheels, and further wherein the wheels have the same outside diameter. The wheels on the left side of the vehicle may be constrained to rotate at a first speed and the wheels on the right side of the vehicle may be constrained to rotate at a second speed, and further wherein the first speed and the second speed are independently selectable by the vehicle operator. The electronic controller may be configured to sequentially poll signals of the four position sensors at a repeating and predetermined time interval, and may be further configured to calculate an average position for each sensor based upon a plurality of polled signals for that sensor. The electronic controller may be configured to independently signal each of the four actuators based upon the average position for the position sensor associated with the wheel such that any combination of the actuators can be engaged to raise or lower their respective wheels.